Role of zinc as an essential microelement for algal growth and concerns about its potential environmental risks.

This work aims to measure the role of zinc as an essential micronutrient for algal growth and the effect of using different concentrations of this heavy metal on growth and essential metabolites of Dunaliella tertiolecta. The EC50 obtained was around 15 mg/l. The results obtained proved that lower concentrations of the element increased growth and the content of the measured metabolites (photosynthesis pigments, fatty acids, and protein) but with different responses. The increase in content of these metabolic products with low concentrations of the tested heavy metal may be attributed to inhibition to these metabolites' export out of cells by heavy metals. The obtained infrared peaks of the major cell constituents of the treated cells revealed the emergence of new peaks and the removal of others, indicating changes in cell constituents due to changing zinc concentrations.

Algal sensitivity to nickel toxicity in response to phosphorus starvation.

In all living cells, phosphorus plays an important function in the transport of metabolic energy and as a structural component of nucleotide and phospholipid molecules. Ni2+ is found in industrial water effluent and has the potential to harm aquatic ecosystems. The study was designed to assess the effect of phosphorous-limiting conditions in combination with the absence or presence of different concentrations of nickel on growth, pigment content, photosynthesis, and respiration activities of the studied alga Dunaliella tertiolecta. The EC50 for dissolved nickel was around 15 mg/L. Results obtained showed that, growth and chlorophyll content under phosphorus limiting conditions increased under low concentrations of dissolved nickel. The amount of O2-evolution with phosphorus limiting conditions was lower than those of untreated normal cultures. Lower dissolved nickel concentrations resulted in higher photosynthesis rates in the treated phosphorus-starved cultures than higher concentrations. The degree of response to metal toxicity in phosphorus-starved medium is depending mainly on the concentration of the element and the length of the culturing period and it was less than those in normal control culture containing phosphorus.

Monitoring effect of nickel, copper, and zinc on growth and photosynthetic pigments of Spirulina platensis with suitability investigation in Idku Lake.

Owing to the increase of pollutant sources in oceans, seas, and lakes, there is an expected effect on growth and metabolism of planktonic algae which are considered primary producers in the ecosystem. Therefore, it becomes urgent to carry out laboratory studies to test to what extent these pollutants can affect the growth of algae which is necessary as a food for marine fishes. Spirulina is considered the most important algal species due to its high nutritional value for humans and animals. Therefore, this work investigated the effect of different concentrations of Ni2+, Zn2+, and Cu2+ metal ion pollutants on growth of the blue-green alga Spirulina platensis. EC50 was identified to be around 2 mg/l for the three heavy metals. The suitability of Idku Lake for Spirulina platensis growth was investigated using multi-criteria spatial modeling integrated with remotely sensed data processing. Spatial distribution maps of turbidity, water nutrients, and phytoplankton were the input criteria used to assess Idku Lake's suitability. The results obtained proved that low concentrations of the tested heavy metals stimulated growth and pigment fractions (chlorophyll a, carotenoids, and total phycobilins content) but to different degrees. The inhibitory effect was more prominent in the case of copper ions than zinc and nickel ions with all concentrations used. The overall suitability map of Spirulina platensis in Idku Lake showed that the whole lake is suitable for growth and proliferation except for the northwestern corner due to the high salinity levels. The present paper helps to understand the behavior of algae responding to environmental pollution, which supports environmental planners with the necessary baseline for investigating the fate of pollutants and the potential risk.

Effect of heavy metals on protein content of marine unicellular green alga Dunaliella tertiolecta.

Microalgae are rich source of protein containing necessary amino acids at different levels. The present study was designed to assess stimulatory and/or inhibitory impact of five different concentrations (5, 10, 15, 20, and 25 mg/L) of three essential heavy metals (nickel, zinc, and copper) on protein content (soluble, insoluble, and total) of the marine unicellular green alga Dunaliella tertiolecta. Further, geospatial analyses were used to assess the suitability of Qaroun Lake for D. tertiolecta proliferation. The experimental results showed a gradual increase in protein content of D. tertiolecta with low concentrations of the three investigated heavy metals. However, increasing levels of heavy metals led to inhibitory effect on protein synthesis in alga with different grades. Ni, Zn and Cu levels in Qaroun lake were found suitable for the proliferation of Dunaliella (Lower than 5 mg/L). The present study highly recommends the necessity to encourage site selection of optimal marine environments suitable for the proliferation of marine algae rich in protein content.